586 J. M. SHERMAN, G. E. HOLM AND "W. E. ALBUS 



slow multiplication of the organisms. This was done in tests 

 in which cultures were incubated at a temperature of 12°C. 

 At this temperature the increments of growth when measured 

 daily are about the same as those taken at hourly intervals at 

 37°C. The results obtained in these tests (experiments 7 and 8) 

 show the same characteristic increase in the velocity of growth 

 with NaCl, and also a well defined shortening of the lag period. 

 The data from experiment 7 are plotted in figure 3. 



SUMMARY 



It has been shown that the accelerating effect of certain salts 

 upon the growth of Bad. coli is due primarily to an increase in 

 the velocity of growth of the organism during the period of maxi- 

 mum multiplication. 



The same salts usually also increase the accelerating effect by 

 decreasing the duration of the preliminary latent period. 



REFERENCES 



Holm, G.E., AND Sherman, J. M. 1921 Jour.Bact., 6, 511. 

 Sherman, J. M., and Holm, G. E. 1922 Jour. Bact., 7, 465. 



APPENDIX 



The organism used in all of these experiments was a laboratory 

 strain of Bact. coli. Inoculations were made from cultures one 

 or more days old in 1 per cent pepton. 



The media used for determining the growth rates were put up 

 in 100-cc. amounts; all contained 1 per cent pepton, with the 

 indicated amount of salt, and were adjusted to a reaction of pH 

 5.4. 



In experiments 1 to 6, incubations were at 37°C. and plate 

 counts were made at hourly intervals. Experiments 7 and 8 

 were conducted at 12°C. and counts made at daily intervals. 



Standard extract-pepton agar was used for plating, and the 

 plates were incubated for three days at 33°C. before counting. 

 TripUcate plates of each dilution were made in every case. 



